PEST NOTES Publication 7425University of CaliforniaStatewide Integrated Pest Management ProgramAgriculture and Natural Resources

September 2009

Two closely related species of long-horned borer beetles (family Ceram-bycidae) attack eucalyptus trees in California. Phoracantha semipunctata (Fig. 1), which is native to Australia, was introduced into Southern Califor-nia in the 1980s. It rapidly became a pest and now appears throughout the state wherever eucalyptus trees grow. Natural enemies were introduced from Australia, and biological control com-bined with improved cultural care of eucalyptus have dramatically reduced the number of trees this borer kills each year.

In 1995, a second species of longhorned borer, Phoracantha recurva (Fig. 1), was discovered in Southern California in Los Angeles, Riverside, Orange, and San Bernardino counties. This beetle has spread throughout much of California wherever eucalyptus grows. However, biological control has been less effective against this new borer. P. recurva, along with several other new pests, can stress and kill eucalyptus.

Freshly cut wood, dying limbs, and trees suffering from stress, especially drought stress, attract both of these beetles. Many eucalyptus trees in Cali-fornia grow in unmanaged or mini-mally managed environments with no irrigation. Eucalyptus species that grow in wetter areas of Australia have been planted in California, so when they experience prolonged dry periods, these species are especially susceptible to being attacked and killed by borers.

IDENTIFICATION AND LIFE CYCLEAdults of the two Phoracantha species resemble each other. Their antennae are as long as or longer than their body, and the antennae of the males have prominent spines. They differ, however,

in the number of hairs on their anten-nae and their wing color. For example, dark brown predominates on the wing covers of P. semipunctata, while yellow to cream color predominates on wing covers of P. recurva (Table 1).

Several nights after emerging from infested wood and mating, the female beetles of P. semipunctata begin laying eggs in groups of 3 to 30 beneath the loose bark or in crevices on bark sur-faces of eucalyptus trees. Females can live 1 or more months and lay up to 300 eggs, which hatch in about 1 to 2 weeks depending on temperature.

After hatching, larvae bore directly into the inner bark, or they feed temporarily on the bark surface before boring in. If feeding on the surface, outward from the egg mass they leave a distinct, dark trail 1/4 inch to several inches long that scores the bark surface (Fig. 2). Most larval feeding occurs in the cambium, the thin layer of tissue on the bark’s inner surface. There larvae bore gal-leries that can extend several feet (Fig. 3). In trees with heavy infestations, the scraping sounds the developing larvae make while chewing in the cambium are audible from a distance of several feet.

At the end of the feeding period, larvae excavate pupal chambers in the wood. They enter the chambers, packing the

Integrated Pest Management for Home Gardeners and Landscape Professionals

Eucalyptus longhornEd BorErs

Table 1. Differences Between Two Eucalyptus Longhorned Borers in California. Characteristic Phoracantha semipunctata Phoracantha recurva

Color of wing covers (elytra)

Mostly dark brown; a zigzag line bisects the cream-colored area in the middle

Mostly cream to yellowish with dark brown areas primarily limited to the rear third

Golden hairs on the underside of each antenna segment

None to sparse Long and dense

Sources: Gill, R. J. 1997. An Australian eucalyptus beetle. California Plant Pest and Disease Report. 16(1–2):12; and Hanks, L. M., T. D. Paine, J. G. Millar, and C. Campbell. Another tree-killing pest of eucalyptus invades California. California Plant Pest and Disease Report. 16(1–2):19–21.

Figure 1. Adult eucalyptus longhorned borers, Phoracantha semipunctata (left) and P. recurva.

Figure 2. Dark trails made by young eucalyptus longhorned borer larvae.

Figure 3. Peeling back this tree’s bark reveals galleries mature larvae made.

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dry leaves, and the bark is cracked and packed with larval excrement. Infested trees usually die within of a few weeks of girdling, although resprouting can occur from the tree base.

MANAGEMENTYou can use the same methods to man-age both Phoracantha species—reduce tree stress, properly handle eucalyp-tus wood, plant resistant species, and avoid activities that disrupt biological control. Pesticide applications gener-ally aren’t effective in managing these pests.

Cultural Management Certain species of eucalyptus are more resistant to longhorned borers, espe-cially those adapted to drier conditions (Table 2). Be aware that a few species such as blue gum (Eucalyptus globulus) have become invasive, and other spe-cies can be better choices for planting depending on the area you live in. Also, longhorned borers can attack any spe-cies of eucalyptus if trees are heavily stressed, such as when planted in poor soil or deprived of sufficient water. A well-maintained tree of a susceptible species can be at less risk of infesta-tion than a neglected tree of a resistant species.

Consider providing supplemental water on a regular schedule during prolonged dry periods, particularly if seasonal rainfall has been below normal. If a tree has received regular irrigation, avoid prolonged interrup-tions to watering, particularly during

holes behind them with frass (excre-ment) and wood shavings (Fig. 4). Lar-vae require about 70 days to develop in fresh wood or logs during hot summer months and up to 180 days in drier logs. Only relatively fresh logs sustain beetle larvae; old, dry logs are too hard for larvae to feed on and then successfully develop. Mature larvae can be more than 1 inch long and are cream colored and legless.

Following pupation, adult beetles emerge from the same holes by chew-ing through the frass plugs. During spring and summer, the beetle requires 3 to 4 months to complete its life cycle, but starting in fall and winter it can require up to 9 months. There are two and possibly three overlapping gen-erations a year. Larvae can be present anytime during the year, and adults can emerge from pupae anytime from April through October.

The life cycle of P. recurva differs somewhat from that of P. semipunctata. P. recurva develops more quickly and completes a generation in a shorter period of time. P. recurva adults can be present for a longer period during the year and emerge as early as February.

DAMAGEHoles in the bark and stains or oozing liquid on limbs or trunks are common symptoms of longhorned borer dam-age (Fig. 5). Foliage can discolor and wilt, and limbs can die back. Long-horned borers usually attack stressed or damaged plants, leaving vigorous, appropriately watered trees alone. In California, however, many eucalyptus trees are seasonally water stressed dur-ing hot summer months, rendering a significant proportion of them suscep-tible to beetle attack. Tree species with some resistance to these wood borers can produce copious amounts of resin in response to an attack.

Extensive larval feeding beneath the bark can spread around the entire cir-cumference of a tree, girdling, or com-pletely removing a strip of bark from, the trunk. Trees at this stage of infesta-tion have a thin canopy with wilted or

Table 2. Relative Susceptibility of Eucalyptus Species to Phoracantha semipunctata.More susceptible More resistant blue gum, E. globulus hybrid, E. trabutii

flooded gum, E. grandis lemon gum, E. citriodora

Karri gum, E. diversicolor mountain gum, E. dalrympleana

manna gum, E. viminalis red ironbark, E. sideroxylon

round leaved/red flowered, E. platypus/nutans river red gum, E. camaldulensis

shining gum, E. nitens sugar gum, E. cladocalyx

Sydney blue gum, E. saligna swamp mahogany, E. robustaAdapted from Hanks, L. M., T. D. Paine, J. G. Millar, and J. L. Hom. 1995. Variation among Eucalyptus species in resistance to eucalyptus longhorned borer in southern California. Entomologia Experimentalis et Applicata. 74:185–194.

Figure 4. Mature larva of the eucalyptus longhorned borer in a cross section of a tunnel. Note that frass packs the entry way.

Figure 5. Holes in trunk ooze with sap, a common sign of a long-horned borer in-festation.

the summer when insect pests are most active. Suddenly cutting off irrigation to trees that have been receiving water regularly will cause trees to become water stressed and susceptible to heavy attack. If irrigating, apply water to the ground below the edge of the outer canopy and not in close near the trunk. Avoid frequent, shallow water-ing, which often occurs for lawns. Such a watering schedule is likely to promote tree root disease.

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The specific amount and frequency of water needed vary greatly depending on the site and tree species. A general recommendation is to irrigate eucalyp-tus trees infrequently (possibly once a month during drought periods) but with sufficient amounts so the water penetrates deeply into the soil (1 foot or more below the surface). You can achieve this by applying water slowly through drip emitters that run continu-ously for several days. In areas without an established irrigation system, you can use a water tank truck to tempo-rarily flood soil. However, avoid pro-longed waterlogging, especially around the root crown, because eucalyptus trees are susceptible to pathogens that cause Armillaria and Phytophthora root rots.

Protect trees from injuries. Remove infested trees and branches immedi-ately, but do all other pruning during December and January when adult beetles aren’t present. When planning extensive limb removal for reasons other than removing dead wood or eliminating hazardous trees, space the trimming over several years. Other-wise, the tree might not have adequate foliage to produce the food it needs to maintain good health. Also, extensive pruning suddenly exposes previously shaded bark to direct sunlight, which can result in sunburn (sunscald) can-kers that are susceptible to borer attack.

Eucalyptus logs used for firewood and dead or dying branches and trees are the beetles’ primary breeding sites. Sanitation is critical for reducing beetle numbers. Until the wood dries below a critical level, it remains highly attrac-tive to egg-laying beetles. Anything you can do to speed the drying process, such as cutting and splitting wood and, even more importantly, remov-ing bark from felled logs, helps reduce the length of time it can support beetle development. If infestation already has occurred, you should treat or destroy the wood. Bury, burn (where permitted), or chip infested eucalyptus. Chipped eucalyptus makes an excellent mulch.

Alternatively, solarize wood by placing it in a sunny location and covering it with ultraviolet-resistant plastic. This prevents new beetles from attacking and resident beetles from emerging and flying to nearby living eucalyptus. You can store properly solarized wood for firewood.

To solarize, tightly seal wood beneath thick (10 mil), clear plastic sheets in a sunny location for several months. To be effective, this treatment requires keeping wood piles small; using high-quality, clear plastic resistant that is to ultraviolet light degradation; thor-oughly sealing the edges; and promptly patching holes to prevent beetles from escaping. For more information on so-larization, see the publications by Don-aldson and Seybold (1998) and Sanborn (1996) in References.

Biological Control Biological control with natural enemies has provided a partial solution to longhorned borer problems. At least one native California wasp, Helcostizus rufiscutum (Ichneumonidae), parasit-izes P. semipunctata but only rarely; consequently, an egg parasite has been introduced from Australia for biologi-cal control.

The wasps are highly specialized para-sites, attacking only certain beetles. They present no threat to humans, pets, or livestock. By reducing beetle popula-tions to a lower level, natural enemies have reduced borer damage, because vigorous trees can survive a few at-tacks.

The egg parasite is Avetianella longoi (family Encyrtidae), a 1/16-inch-long, host-specific, introduced wasp that lays its eggs within the eggs of the beetles. Parasitized eggs develop brown shells through which you can observe the body and dark eye spots of developing wasps. A. longoi disperses rapidly and efficiently finds borer eggs. This wasp has become widely established in Cali-fornia, typically attacking and killing more than 90% of P. semipunctata eggs in the field. However, it is less effective against the more recently introduced

OTHER EUCALYPTUS PESTSSeveral other introduced insects also attack eucalyptus. Pest managers should learn how management methods such as conserving natural enemies and planting resistant species can help control these pests, which include leaf-feeding beetles (tortoise beetles), eucalyptus gall wasps, and at least six species of psyllids.

Some of these insects now are now un-der effective biological control, including the bluegum psyllid (Ctenarytaina eu-calypti), the eucalyptus snout beetle or gumtree weevil (Gonipterus scutellatus), and especially in Southern California the eucalyptus redgum lerp psyllid (Gly-caspis brimblecombei). Inappropriate actions such as spraying persistent, broad-spectrum insecticides—those that remain in the environment at levels toxic to natural enemies for more than a few days—can harm natural enemies and can cause outbreaks of these other pests.

For more information, see:• Pest Notes: Psyllids. http://www.ipm.

ucdavis.edu/PMG/PESTNOTES/pn7423.html

• Pest Notes: Eucalyptus Redgum Lerp Psyllid. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7460.html; and

• Pest Notes: Eucalyptus Tortoise Beetles. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74104.html.

Figure 6. Healthy (yellow) and parasit-ized (orange) eggs.

P. recurva. Conserve parasites by avoid-ing the spraying of eucalyptus bark or foliage with broad-spectrum, persistent insecticides.

Figure 6 shows an example of healthy, yellow eggs compared to parasitized eggs.

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Chemical Control Early work from both California and other regions where beetles have be-come established indicated insecticides might not be suitable for managing eu-calyptus longhorned borer populations, but more recent studies indicate newer, systemic insecticides (compounds that move within trees after being applied to the soil) might protect individual trees if applied before beetle colonization. Ex-ercise care when using any insecticide, because of the potential for drift, envi-ronmental impact, effects on beneficial or nontarget insects, and risk of expo-sure to humans in urban environments.

Borer management must focus on bio-logical control and cultural practices and environmental conditions that favor the tree to the disadvantage of the beetle. Because natural enemy in-troductions by government agencies and university scientists are funded through taxes, public and professional support is critical to the ongoing suc-cess of biological control.

REFERENCESDonaldson, S. G. and S. J. Seybold. 1998. Thinning and Sanitation: Tools for the Management of Bark Beetles in the Lake Ta-hoe Basin. Reno: Univ. of Nev. Coop. Ext. Publ. FS-98-42. Also available online, http://www.unce.unr.edu/publications/files/ho/other/fs9842.pdf. Accessed Sept. 9, 2009.

Dreistadt, S. H., J. K. Clark, and M. L. Flint. 2004. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 3359.

Paine, T. D., J. G. Millar, and L. M. Hanks. 1995. Integrated program pro-tects trees from eucalyptus longhorned borer. Calif. Agric. 49(1): 34–37.

Sanborn, S. R. 1996. Controlling Bark Beetles in Wood Residue and Firewood. Sacramento: Calif. Dept. of Forestry and Fire Protection, Tree Notes 3. Also available online, http://ceres.ca.gov/foreststeward/pdf/treenote3.pdf. Ac-cessed Sept. 9, 2009. v

AUTHORS: T. D. Paine, Entomology, UC Riverside; S. H. Dreistadt, UC Statewide IPM Program, Davis; and J. G. Millar, Ento-mology, UC Riverside.

TECHNICAL EDITOR: M. L. Flint

EDITOR: M. L. Fayard

ILLUSTRATIONS: Figs. 1–3 and 5–6, J. K. Clark; Fig. 4, P. Svihra.

This and other Pest Notes are available atwww.ipm.ucdavis.edu.

For more information, contact the University ofCalifornia Cooperative Extension office in your county. See your telephone directory for addresses and phone numbers, or visit http://ucanr.org/ce.cfm.

University of CaliforniaAgriculture and Natural Resources Program

Produced by UC StatewideIntegrated Pest Management ProgramUniversity of California, Davis, CA 95616

University of California scientists and other qualified professionals have anonymously peer reviewed this publication for technical accuracy. The ANR Associate Editor for Urban Pest Management managed this review process. To simplify information, trade names of products have been used. No endorsement of named products is intended, nor is criticism implied of similar products that are not mentioned. This material is partially based upon work supported by the Extension Service, U.S. Department of Agriculture, under special project Section 3(d), Integrated Pest Management.

WARNING ON THE USE OF CHEMICALS Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original, labeled containers in a locked cabinet or shed, away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. Do not place containers containing pesticide in the trash or pour pesticides down the sink or toilet. Either use the pesticide according to the label, or take unwanted pesticides to a Household Hazardous Waste Collection site. Contact your county agricultural commissioner for additional information on safe container disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that they may contaminate water supplies or natural waterways.

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